Circuit breaker



May 4, 1943- M. G. LEONARD 2,318,085

CIRCUIT BREAKER Filed Sept. 19, 1940 Y 3 Sheets-Sheet l May 4, 1943, M.G. LEoNARD CIRCUIT BREAKER Filed Sept. 19, 1940 5 Sheets-Sheet 2INVENTOR /Verr/V/ 6 e0/fara."

BY q (\TTORN% WITNESSES: l

May 4, 1943. M. G. I EoNARD 2,318,085

C IRCUI T BREAKER Patented May 4, 1943 CIRCUIT naman Merrill G. Leonard,Sharon, Pa., .assigner to Westinghouse Electric & Manufacturing Company,East Pittsburgh, Pa., a corporation of Pennsylvania ApplicationSeptember 19, 1940, Serial No. 357,391

(Cl. V200-116) 12 lClaims.

The invention relates to circuit interrupters and more particularly tomultipole circuit breakers of the type which are manually operableandalso automatically operable in response to predetermined abnormalconditions.

The present invention in certain respects constitutes a furtherdevelopment and improvement of the circuit breaker disclosed in mycopendingy application Serial No. 163,202, illed September 10. 1937,assigned to the assignee of this invention, and now Patent No.2,227,506, issued January 7, 1941.

An object of the present invention is the provision of an improvedmultipole circuit breaker that is simple, compact, and inexpensive tomanufacture.

Another object of the invention is the provision of a multipole circuitbreaker embodying an individual actuating mechanism and trip means forthe contacts of each pole, with means which utilize the energy releasedduring or after tripping of any one poleto automatically trip the otherpoles.

Another object ofthe invention is the provision oi' an improvedmultipole circuit breaker having an individual actuating means and tripmeans for the contacts of each pole, and a novel interlocking meansoperable when any pole of the breaker trips to automatically effecttripping of the other poles. 4

Another object of the invention is the provision of a multipole circuitbreaker having an individual actuating means and trip means for thecontacts of each pole, and an interlock which utilizes the kineticenergy oi' the moving contact arm of whichever pole is tripped at theend of its opening motion to automatically trip theother pole or poles.

Another object of the invention is the provision of an improvedmultipole circuit breaker mechanism in which the opening movement oi thecontact arm of any pole upon tripping there- 'of is utilized to move-theelectroresponsive trip element of the other pole to automaticallytripthe other pole.

Another object of'the'invention is the provision of a circuit breakerwith a novel self-aligning 'contact means of simplefand inexpensiveconstruction.

The novel features that are considered chal'-l acterlstic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to construction and opthe parts beingshown in the closed circuit position;

Fig. 3 is a fragmentary perspective view of the circuit breakermechanism:

Fig. 4 is an enlarged view, partly in section, of the contact means andswitch arm of the breaker; and v Fig. 5 is a sectional view similar toFig. 1 showing the position of the parts when one pole of the breakerhas been tripped.

Referring to the drawings, the circuit breaker illustrated isof thetwo-pole type and includes a housing 9 of molded insulating materialwhich serves to support and enclose the various parts of the circuitbreaker mechanism. The housing is divided into two compartments by alongitudinal partition formed integral with the housing to providechambers for the mechanisms of the two poles of the breaker. The twopoles of the circuit breaker are substantially identical inconstruction, and hence a detailed description of only one pole will begiven, since it is believed that it will be suillcient for a clearunderstanding of the invention.

Each pole of the circuit breaker comprises in general a stationarycontact Il, a cooperating movable contact i3 carried by a movable switcharm'i5, actuating means indicated generally at I1 for moving the switcharm to open and closed circuit position. and a trip device indicatedgenerally at. I9 which is operable in response to predetermined currentconditions vin the circuit of its pole to cause the actuating means toautomatically open the contacts.

I'he stationary contact il is secured tothe inner angularly'bent end oi'a terminal conducting strip 2i, which is secured to the end wall of thehousing by suitable rivet fastening means 23. The opposite end of theterminal conducting strip 2l is angularly bent, andextends outside ofthe housingl 9 for connecting the breaker tc an external electricalcircuit.

The movable contact i3 is carried by the switch arm i5 which isgenerally U-shaped, as best shown in Fig. 3. The switch arm l5 isstamped "from sheet metal, and is bent to provide a pair of parallellegs 25 (Fig. 3) and -a bight portion 2l. The movable contact i3 ismounted on a projection 23 which is formed integral with the switch armi5. The bight portion 2l of the switch arm I5 is provided with anextension 3l which has a'par of lugs 33 extending -laterally from thesides/thereof and formed integral therewith for a purpose which will behereinafter described.

The actuating means for the movable contact I3 comprises in general apivoted releasable member 35 to which the switch arm i5 is pivoted, a

Fig. 2 is a front elevational view oi' the circuit movable operatingmember 31, and an overcenter sprirg 39 connecting the operating memberand the bight portion 21 of the switch arm I5.

'Ihe pivoted releasable member 35 is stamped from sheet metal plate andformed to provide a pair of spaced parallel legs 4I (Fig. 3) which arejoined by a 'bridge portion 45 at the inner end. The releasable member35 is pivotally supported by means of a pivot pin 41, the ends of whichare removably engaged in suitable bearing recesses 49 (Fig. 1) formed inthe insulating material of the housing. The switch arm I5 is nestedwithin the legs 4I of the releasable member 35, and is pivoted to thereleasable member by a pair of vshort pivot pins 53. It will thus beseen that the releasable member 35 and the switch arm I5 connectedthereto are removably mounted in the housing 9, and these elements areadapted'to be retained in mounted position by means of the overcenterspring 39.

`|The operating member 31 is also stamped from sheet metal plate andformed to provide a pair of outstanding legs 55 (Fig. 2) which areprovided with openings for engaging a common operating member which willbe hereinafter described. The operating member 31 is provided thereleasable member 35 to its latched position when the operating memberis manually moved upwardly beyond its normal open position following atripping operation.

The trip device I9 comprises a U-shaped bimetallic trip element 69 whichhas its bight portion 1I (Fig. 3) secured to a pivoted adjusting arm 13by means of a plurality of rivets 15. The lower ends of the legs of thetrip element 69 have an insulating block 11 secured thereto by pivotallymounted in the housing 9, and it will at each end with a pair of lateralprojections 59 (Fig. 2) which are adapted to slide on spaced parallelarcuate surfaces 6| formed on the molded housing. Suitable ribs 62 (Fig.2) are provided on the housing adjacent the arcuate guide surfaces 6|for guiding the operating member 31 land preventing lateral displacementthereof.

The operating member 31 and the bight portion 21 of the switch arm l5are perforated to receive the hook ends of the overcenter spring 39. Theovercenter spring 39 is held in tension between the switch arm I5 andthe operating member 31, and thus serves to maintain the pivotedreleasable member 35 and the operating member 31 in mounted position inthe molded housing.

'I'he spring 39 is disposed between the legs of the switch arm l5 andthe legs of the pivoted releasable member 35, and in the closed circuitposition of the breaker the line of action of the spring 39 is sodisposed relative to the pivot axis 41 of the releasable member 35 thatit tends to bias the releasable member in an upward or clockwisedirection about the pivot axis 41. The releasable member 35 is normallyheld in the latched position shown in Fig. 1 by means of thecurrent-responsive trip device I9, the bridging portion 45 of thereleasable member 35 being provided with a latch projection 63 whichnormally engages a latch 65 carried by the trip device.

The downward' movement of the operating member 31 is limited by a pairof stops 66 (Fig. 2) adjacent the arcuate surfaces 6I. The stops 66 areadapted to be engaged by the upper lateral projections 59 of theoperating member 31 in the closed circuit position of the operatingmember, as shown in Fig. 2. Upward movement of the operating member 31is limited by the engagement of the lower lateral projections 59 of theoperating member with a pair of projections 61 formed on the legs 4| ofthe pivoted releasable member 35. The projections 61 extend through theopening in the housing between the sides of the operating member 31 andthe arcuate surfaces 6| as best shown in Fig. 2.

The projections 61 of the releasable member 35 and the lower lateralprojections 59 of the operating member 31 form a means for resetting beseen that rotative movement of the adjusting arm 13 about the pivot 85will change the position of the latch 65 with respect to the latchprojection 63 of the pivoted releasable member 35.

The right-hand end of the adjusting arm 13 is notched to receive anadjusting screw 89 which passes through a transverse partition wall 9|formed in the housing 9. 'Ifhe screw 89 is held in mounted position onthe partition wall 9| by means of a nut 93. A tubular adjusting nut 95is threaded on the end of the screw 89, and this nut engages the notchedend of the adjusting arm 13. The tubular nut 95 is provided with aknurled portion 91 which extends through an opening 96 provided thereforin the upper end wall 99 of the housing to provide for manual adjustmentof the nut 95.

A coil compression spring |03 encircles the screw 89 and engages thenotched end of the. adjusting arm 13 at one end and the transversepartition wall 9| at its other end. The spring |03 serves to maintainthe notched end of the adjusting arm 13 in engagement with the tubularadjusting nut 95.

From the foregoing description of the trip device, it will be apparentthat when the nut 95 is screwed down it will move the adjusting arm 13and bimetal trip element 69 in a clockwise direction about the pivot 85,and thereby decrease the amount of overlap between the latch carried bythe bimetal trip element 69 and the latch projection 63 of thereleasable member 35. This will cause thel breaker to be tripped inresponse.

to a lower magnitude overload. Conversely, when the nut 95 is screwedout, that is, backed off, the

'effect tripping of the breaker.

As has previously been mentioned, the structures of the two poles ofthebreaker are identical, and are insulated from lone another by acentrally disposed longitudinal partition wall I 0 formed in the housing9. The operating members 31 for the two poles are connected forsimultaneous movement together by a common operating member I ofinsulating material. The common operating member I Il is in the form ofa yoke. rand the opposite arms thereof extend through the openingsprovided therefor in the two operating members 31. An operating rod (notshown) is adapted to be connected to the central portion' of lthe commonoperating member III.

A cover I|1 of molded insulating material is removably secured to thehousing 9 for the purpose of enclosing and protecting thecurrentresponsive trip devices I9. The cover II1 is provided with acentral longitudinal partition |I9 which aligns with the partition III)formed in the housing 9 so as to completely isolate the two poles of thebreaker from one another.

The circuit for each pole of' the breaker is the same and extends fromthe lower terminal strip 2|'through the stationary contact II, themovable contact I3, and a flexible shunt conductor |23 connected to themovable contact, to one leg of the bimetal trip element 69, and throughthe bimetal trip element 69 and a flexible shunt conductor |25 to anupper terminal strip |21 (Fig. 2), the end of which extends outside ofthe casing on the side thereof.

Referring to Fig. 4, the movable contact I3 is mounted on the switch armI5 for limited tilting f or swiveling movement relative thereto, so asto permit the contact to seat flat against the stationary contact II..For this purpose, the movable contact I3 is provided with a reducedcylindrical portion |29 between the front and back thereof, and isformed to provide substantially spherical shoulders |3| adjoining thereduced portion. The movable contact is loosely retained in a C-shapednotch |33 provided therefor in the lower projection 29 of the switch armI5. The

extending fingers |35 forming the notch are bent toward each otherslightly to retain thecontact I3 in the notch. The fingers, however, arenot bent far enough to bind the contact. The flexible shunt conductor|23, which connects the movable contact to one end of the bimetal tripelement 69, is rigidly attached at its other end to the back of themovable contact I3, and extends through and is firmly held in a bushing|31 which is mounted in a notch provided in the bight portion 21 of theswitch arm I5.

The spherical shoulders |3I permit the movable contact I3 to tilt orswivel a slight amount, so as to seat fiat against the stationarycontact when it is moved to closed circuit position.

The circuit breaker is provided with an interlock mechanism designed sothat when either pole of the breaker trips the other pole will alsotrip. The interlock mechanism utilizes the kinetic energy of either ofthe switch arms I5 i,

of insulating material which is transversely disposed in the upperportion of the housing 9 between the partitionwall 9| and the upper endwall 99 of the housing. The bar |39 is pivotally mounted intermediateits ends on a rod I4| which is mounted in the housing 9. The rod |4| hasits inner end engaged in a bearing provided therefor in the mid portionof the bar |39, and the other end is bent upwardly at a right angle andextends through a notch |43 (Fig. 2) provided therefor in the upper endwall 99 of the housing. The angularly bent end of the pivot rod |4I issecurely retained in the notch |43 by a pair of nuts |45 which arethreaded on the rod and engage the opposite sides of the end wall 99, asshown in Fig. 2. y

The opposite ends of the insulating bar |39 are disposed directly abovethe notched ends of the adjusting arms 13 on'the side thereof oppositethe coil springs |03. The opposite ends of the bar |39 engage the headsof a pair of pins y 63, andthe corresponding switch arm I5 is causedv ycauses the insulating bar |39 justing arm |41 which are slidably mountedin openings provided therefor in the partition wall 9|. The pins |41extend through the notches in the ends of the adjusting arm 13, and theheads of the pins are disposed ybetween the adjusting arm 13 and theinsulating Ibar |39. The lower ends of the pins |41 project through thetransverse partition wall 9|, and are disposed to be engaged and movedby angularly bent projections |49 of the switch arms I5 as the switcharms approach the tripped open position.

When either pole of the circuit breaker is tripped in response topredetermined overload conditions, the releasabie member 35 of theaffected pole is released by the tripping of the latch to move to atripped open circuit position, as shown in Fig. 5. As the switch arm I5approaches the tripped open position, the projection I 49 thereofstrikes the pin |41 and the impact to rotate on the pivot |4I, thuspushing the adjusting arm 'I3 of the other pole. This causes rotationo1' the ad` 13 of the other pole aboutits pivot 85, moving the bimetaltrip element 69 and latch 65 to release the releasabie member 35 of theother pole to cause tripping thereof. When the circuit breaker ismanually operated to the opencircuit position, the projections |49, asshown dotted in Fig. I, do not engage the pins |41, and hence theinterlock bar |39 is not affected by manual opening of the circuitbreaker.

The operation of the circuit breaker is briefly as follows: To manuallyopen the circuit breaker, the common operating member III is moved in anupward direction to effect simultaneous upward movement of the twooperating members 31 which are connected thereto. The upward movement ofthe operating members 31 moves the line of action o1' the overcentersprings 39 across and above the pivot axis 53 of the switch arms I5. Assoon as the line of action of the overcenter springs crosses above thepivot axis 53, the springs act to move the twoswitch arms I5simultaneously to the open circuit position, indicated by the dottedlines in Fig. 1. This movement of the switch arms takes place with asnap action.

To manually close the circuit breaker, the common operating member I Iis moved downwardly to effect simultaneous downward movement of the twooperating members 31. The downward movement of the operating members 31moves the line of action of the overcenter springs 39 across and belowthe pivot axis 53 of the switch arms I5. As soon as the line of actionof the overcenter springs 39 crosses below the pivot axis 53,

the springs act to move the switch arms I5 to the closed circuitposition shown in Fig. 1 with a snap action.

When an overload of predetermined magnitude and duration occurs in thecircuit through either pole of the circuit breaker, the bimetal tripelement 69 of' the affected pole is heated thereby a sufficient amountto deflect in a direction away from the actuating means. This deflectionof the trip element causes the latch 65 to disengage the latchprojection 63`of the releasabie member 35, effecting release of thereleasabie member. The overcenter spring 39 of the affected pole thenmoves the pivoted releasabie member 35 in a clockwise direction aboutits pivot -axis 41 from the position shown in Fig. 1 to the positionshown in Fig. 5. During this movement, the legs 4I of the pivotedreleasable member 35 engagethe lateral projections theswitch arm tion,as shown in Fig. contacts.

As has previously been described, the tripping of either pole ofthe'circuit breaker will operate through the interlock bar |39 to alsoeiect tripping of the other pole of the breaker. v As the switch arm 5of the pole on which initial tripping occurs approaches its tripped opencircuit position, the projection |49 thereof strikes the pin l|4`| onthatpole and the impact causes rotation of the interlock bar |38 aboutits pivot |4|. The oppositeend of the bar |39 pushes the'adjusting arm13 of the trip element of the other pole inwardly,'causing rotationofthe adjusting arm T3 andl thel bimetal trip element 69 about thepivot85 to effect/'release of the releasable member 35, thereby tripping theother pole of the circuit breaker. v

Before the circuit breaker can be reclosed following a trippingoperation, it is necessary to reset the pivote'd releasable members 35to their 33 of the switch arm l5 yand move to the tripped open circuitposi- 5, to effect opening o f the latched position. To yreset thecircuit breaker,

the common operating member is moved in anupward direction slightlybeyond thenormal open positionV thereof.A During this movement, thelower lateral projections 59 of the operating members '31 engage theprojections B1 of the pivoted releasable members 35, and effect movementof the releasable members in acounterclockwise direction about theirpivot axes 41 to return the releasable members `to their latchedposition. After the pivoted releasable members have thus been returnedto latched'position, the breaker may beA manually closed in the mannerpreviously described. j l

While the invention has been disclosed in accordance with the provisionsof the patent statutes, it is to be understood that various changes inthe structural details thereof maybe made without departing from' someof the `essential features of the invention. It isl desired, therefore,that the language of the appended claims be .given the broadestreasonable construction permissible inthe light of the prior art. Iclaim as my invention:

1. A multiple circuit breaker comprising a movable contact arm for eachpole, actuating means for each contact arm comprising an overcenterspring for moving the contact arm toopen and to closed circuit positionwith a snap action and a current-'responsivetrip element operable tocause movement of the contact arm to open circuit position, meansoperable by the opening movement of the contact arm of any pole whentripped for causing movement of the currentresponsive trip element oftheother of the poles to trip the other of the poles. y

2. A multipole circuit breaker comprising a set of separable contactsfor each pole, an actuating means for the contacts of each poleincluding a current-responsive tripping means operable to causeautomatic opening of the contacts of its pole, and means comprising aninterlock bar pivoted intermediate its ends for movement in a plane atright angles to thez plane of movement of the movable contacts anddisposed to be moved by the opening movement of the actuating meansofany pole upon tripping thereof to cause tripping of the other of thepoles.

3. A multipole circuit breaker comprising a set of contacts and amovablecontactarm for each pole, an actuating means for each contact armincludingv a member releasable to cause automatic'circuit openingoperation of said contact arm and a. pivotally mountedcurrent-responsive trip element operable in response to predeterminedcurrent conditions in the circuit through its pole to effect release ofsaid releasable member; and means comprising an interlock bar pivotedintermediate its ends disposed to be moved by the opening movement ofthe contact arm of any pole upon tripping thereof to move the tripelement of the other of the poles about its pivot to effect trippingofthe other of the poles.

4. A multipole circuit breaker comprising a` set of separable contactsfor each pole, an actuating means for each set of contacts for. openingand closing the same and a pivotally mounted current-responsive bimetaltrip element for each of a plurality of the poles deectable in responseto predetermined current conditions in the circuit of its pole to causeautomatic opening of the contacts of its pole, a separate adjustingmeans for each bimetal trip element for moving the bimetal element aboutits pivot to adjust the trip characteristic of the corresponding pole ofthe breaker, and means operable by the opening movement of the actuatingmeans of any pole Whentripped to move the bimetal trip element of otherof the poles about its pivot to eiect tripping of other of the poles.

5.` A multipole circuit breaker comprising a set of separable contactsand a movable'contact arm therefor for each pole, an actuating means foreach contact arm comprising an overcenter spring operable to move saidcontact arm to open and to closed circuit position, a member releasableto cause movement of said contact arm to open circuit position, and acurrent-responsive trip element for each of a plurality of the polesoperable in response to predetermined current conditions in the circuitof its pole to effect release of said releasable member vand therebycause movement of thecontact arm of its pole to open circuit position,manually operable means for moving said overcenter springs to manuallyactuate said Contact arms, and means operable by the opening movement ofthe v contact arm of any pole when tripped to cause the currentresponsive trip element -of other of said poles to release itscorresponding releasable member and thereby trip the other of saidpoles.

6. A multipole circuit breaker comprising a set of separable contactsand a movable contact arm therefor for-each pole, an actuating means foreach contact arm comprising an overcenter spring operable to move saidcontact arm to open and to closed circuit position, va member4releasable to cause movement o f said contact arm to open circuitposition, and a currentresponsive trip element operable in response topredetermined current'conditions in the circuit of its pole to eiectrelease of said releasable member and thereby cause movement of thecontact arm of its pole to open circuit position, manually operablemeans for moving said overcenter springs to manually actuate saidcontact arms, and means comprising an interlock bar disposed to be movedby the contact arm of any pole when tripped to move thecurrent-responsive trip element of other of the poles to tripA saidother of the poles.

7. A multipole circuit breaker comprising a'set of separable contactsand a movable.contact arm therefor for each pole, an actuating means foreach contact arm comprising an overcenter spring operable to move saidContact arm to open and to closed circuit position, a member releasableto cause movement of said contact arm to open circuit position, and apivoted currentresponsive trip element for each of a plurality of thepoles operable in response to predetermined current conditions in thecircuit of its pole to effect release of said releasable member andthereby cause movement of the contact arm of its pole to open circuitposition, manually operable means for moving said overcenter springs tomanually actuate said contact arms, and means comprising an interlockbar pivoted intermediate its ends disposed to be moved by the openingmovement of the contact arm of any pole when tripped to cause release ofthe releasable member of other of the poles to thereby eiect tripping ofother of the poles.

8. A multipole circuit breaker comprising a set of separable contactsand a movable contact arm therefor for each pole, an actuating means forthe contact arm of each pole comprising a releasable member pivoted on astationary support, said contact arm being pivotally supported on saidreleasable member, an overcenter spring connected to the contact armoperable to move the contact arm to open and to closed circuit positionwhile said releasable member remains stationary, said pivoted releasablemember being normally restrained and being moved by said spring whenreleased to cause automatic movement of the contact arm to open circuitposition, and a current-responsive trip element operable in response topredetermined current conditions in the circuit through its pole toeffect release of the releasable member of its pole, and meanscomprising a bar which is moved during the opening movement ofthecontact arm of either pole upon tripping thereof to eiect tripping ofthe other pole.

9. A multipole circuit breaker comprising a set of separable contactsand a movable contact arm therefor for each pole, an actuating means forthe contact arm of each pole comprising a pivoted releasable member towhich the contact arm is pivoted, an overcenter spring connected to thecontact arm operable to move the contact arm to open and to closedcircuit position, said pivoted releasable member being normallyrestrained and being moved by the spring -when released to causeautomatic movement of the contact arm to open circuit position, and apivoted current-responsive bimetal trip element.

carrying a. latch for normally restraining said releasable member, saidbimetal trip element being operable in response to predetermined currentconditions in the circuit of its pole to flex without pivoting and eiectrelease of the releasable member of its'pole, the contact arms andactuating means of the several poles being disposed side by side,manually operable means for moving said overcenter springs to actuatesaid contact arms, and means comprising an interlock bar disposed to bemoved by the opening movement of the contact arm of either pole whentripped to move the bimetal trip element of the other pole about itspivot to effect tripping of the other pole.

10. In a multipole circuit breaker, relatively movable contacts for eachpole comprising a stationary contact and a cooperating movable contactcarried by a movable contact arm, an actuating means for each contactarmfor moving able in response to predetermined current conditions in thecircuit of its pole to ex Without pivoting and effect release o thereleasable member of its pole, the contact means and actuating means ofthe several poles being disposed side by side, and means comprising atransversely disposed bar pivoted intermediate its ends about an axisparallel to the plane of movement of the contact arms and movable by theopening movement of the contact arm of either pole when tripped to movethe bimetal trip element of the other pole about its pivot to effecttripping of the other pole.

l1. A multipole circuit breaker comprising a set of separable contactsand a movable contact arm therefor for each pole, an actuating means foreach contact arm for moving the contact arm to open and to closedcircuit position, the actuating means of each of a plurality of thepoles including a member releasable to cause movement of the contact armto open circuit position and a pivoted current-responsive bimetal tripelement carrying a latch for normally restraining the actuating memberand having an arm held in engagement with an adjusting element by aspring, said bimetal trip element being operable in response topredetermined current conditions in thev circuit of its pole to exWithout pivoting and eiect release of the releasable member of its pole,the contact means and actuating means of the several poles beingdisposed side by side, and means comprising a transversely disposedinterlock bar movable by the opening movement of the contact arm of anypole when tripped to move the bimetal trip element of other of the polesabout its pivot to effect tripping cf other of the poles, said interlockbar being pivoted intermediate its ends about an axis parallel to theplane of movement of the contact arms and engageable with the arms ofsaid bimetal trip elements on the side opposite the springs.

12. A multipole circuit breaker comprising a movable contact arm foreach pole, an actuating means for each contact arm for moving thecontact arm to open circuit position, each actuating means including aspring biased member mounted for movement independently of and relativeto said contact arm and releasable to cause automatic operation of thecontact arm to open circuit position, a spring for actuating saidreleasable member and said contact arm, a latch for normally restrainingthe releasable member, and a 'current-responsive trip element operablein response to predetermined current conditions in the circuit of itspole to operate the latch and effect release of the releasable member ofits pole, means operable by the kinetic energy of either contact arm atthe end of its opening movement following tripping thereof for operatingthe latch of the other pole to disengage the releasable member of saidother polesand thereby eiect tripping of said other pole.

MERRILL G. LEONARD.

